ABSTRACT- The Mediterranean area is one of the most intriguing places on Earth where geodynamics and volcanoes are strictly related, and evolved through time. The complexity of the tectonic setting is further enriched by the observed shift of the petrochemical affinity of magmas, in the same volcanic area, from subduction-related to intraplate. The successive opening of back-arc basins (e.g., Ligurian-Provençal basin, Tyrrhenian Sea), following the roll-back of the subducting Adria Plate, produced a migration of magmatism to form a transitional eastward pattern of volcanoes both onshore and offshore.
The Mio-Pliocene volcanic rocks occurring in the Central Mediterranean area are characterised by exceptional variability of the petro-chemical and isotopic features, which allow the distinction of several sectors, when also the areal distribution is considered.
Thus, the Mediterranean area has always been site of studies focused on magma genesis and on the geodynamic significance of the complex scenario achieved through time. In the scientific literature, a large number of papers were published on the magmatism of each single volcanic association/area, but very few dealt with the general picture of the offshore magmatic and geodynamic evolution. The aim of this chapter is to provide an outline of the most prominent geological, petrological, geochemical and isotopic characteristics of the submarine volcanic centres found in the Central Mediterranean basin, with the aim of providing a fairly complete picture of the existing relationships
between the geodynamics and the igneous petrology in this area.
KEY WORD: Central Mediterranean, Tyrrhenian Sea, geodynamic and magmatic evolution, volcanic seamount sectors, subduction.
RIASSUNTO - L’area del Mar Mediterraneo rappresenta una delle più interessanti dimostrazioni sulla Terra di quanto geodinamica e attività vulcanica siano strettamente interconnesse, sia nello spazio che nel tempo. Il complesso assetto tettonico generale di questo areale è ulteriormente arricchito dalla variazione di affinità petro-chimica dei magmi da ambiente di subduzione a intra-placca, anche all’interno della stesse aree vulcaniche. L’apertura dei bacini di retro-arco (e.g., bacino Liguro-Provenzale, Mar Tirreno) che ha seguito l’arretramento della Placca Adria in subduzione, ha indotto la migrazione del magmatismo verso Est come evidenziato dalla distribuzione areale dei vulcani continentali e sottomarini.
Le rocce vulcaniche Mio-Plioceniche dell’area Centro-Mediterranea sono distinte da caratteristiche petro-chimiche e isotopiche eccezionalmente variabili. Tali caratteristiche permettono di riconoscere e delimitare i diversi settori, quando anche la distribuzione areale viene considerata.
Pertanto, l’area Mediterranea è sempre stata oggetto di numerosi studi relativi alla genesi dei magmi e volti all’interpretazione del complesso scenario geodinamico che si è sviluppato nel tempo. Tra
Geodynamics and magmatism of the Central Mediterranean region
Geodinamica e magmatismo della regione Centro-Mediterranea
CASALINI M.(1), PENSA A.(2), AVANZINELLI R.(1)(3),
GIORDANO G.(2), MATTEI M.(2)*, CONTICELLI S.(1)(3)(4)
(1) Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Giorgio La Pira, 4, I-50121, Firenze, Italy.
(2) Dipartimento di Scienze - Geologia, Università degli Studi di Roma Tre, Largo S. Leonardo Murialdo, 1, 00146, Roma, Italy.
(3) Istituto di Geoscienze e Georisorse, U.O.S. di Firenze, C.N.R., Via Giorgio La Pira, 4, I-50121, Firenze, Italy.
(4) Istituto di Geologia Ambientale e Geoingegneria, Area della Ricerca di Roma 1- Montelibretti, Via Salaria km 29.300, I-00015, Monterotondo, Italy.
(*) Corresponding author: mattei@uniroma3.it
questi lavori scientifici, la maggior parte è incentrata sul magmatismo di una singola area o associazione vulcanica mentre solo una minima parte fornisce un quadro generale dell’evoluzione geodinamica e magmatica dei vulcani sottomarini.
Lo scopo di questo contributo è quindi proprio quello di fornire un inquadramento complessivo delle principali caratteristiche geologiche, petrologiche, geochimiche e isotopiche dei centri vulcanici sottomarini che si ritrovano nel bacino del Mediterraneo Centrale. L’obiettivo principale che ci proponiamo è quello di fornire un quadro completo delle relazioni esistenti tra geodinamica e petrologia delle rocce ignee in quest’area.
PAROLE CHIAVE: Mediterraneo Centrale, Mare Tirreno, evoluzione geodinamica e magmatica, settori di seamount vulcanici, subduzione.
1. - INTRODUCTION
The Italian volcanic seamounts lie within the Cen-tral Mediterranean area, located along the conver-gent margin between Eurasia and Africa plates. In the Central Mediterranean, the Africa and Eurasia plates underwent several hundred kilometres of con-vergence since the early Tertiary.
Such a convergence has been mainly achieved by north-westward dipping subduction of the Ionian-Adriatic lithosphere beneath the Eurasia plate. Trench retreat and the progressive fragmentation of the Adriatic-Ionian slab have characterized the Cen-tral Mediterranean subducting system (e.g., PATACCA
et alii, 1992; FACCENNA et alii, 1997, 2001A, 2015; CIFELLI et alii, 2007 and references therein). Presently, evidences for active narrow slabs is given by sub-crustal earthquakes occurring down to 90 km depth below the Northern Apennines (SELVAGGI& AMATO, 1992), whereas a well-defined Benioff zone down to about 670 km, reveals a direct trace of a still active process of lithospheric subduction from the Ionian foreland below the Calabrian Arc and Tyrrhenian Sea (e.g., ANDERSON& JACKSON, 1987; SELVAGGI& CHIARABBA, 1995).
Slab roll-back and the decreasing in width of the active trench through time resulted in the formation of orogenic belts with very tight curvatures (Apen-nines, Calabrian Arc and Sicily)(MATTEIet alii, 2004; CIFELLIet alii, 2007, 2008), together with extensional back-arc basins (Ligurian-Provençal and Tyrrhenian basins; BOCCALETTI& GUAZZONE, 1974; ALVAREZet
alii, 1974), which have been characterized by the
em-placement of medium to large plutonic bodies and by a long-standing volcanic activity that continues up today (e.g., BARBERIet alii, 1973; CIVETTAet alii,
1978; SERRI et alii, 1993, BECCALUVA et alii, 1994; CONTICELLIet alii, 2002; 2017; PECCERILLO, 2017).
In step with back arc basin development, the sub-duction-related island arc volcanism migrated from west to south- east, from Sardinia (32 - 13 Ma) to the currently active Aeolian island arc (Serri, 1997, and references therein). In this subduction system, trench retreat was particularly fast over the Neogene and early Quaternary (PATACCAet alii, 1990) as indi-cated by high extension rates (50 - 70 mm/yr) recorded in the new-formed Vavilov (Neogene) and Marsili (Early-Middle Pleistocene) oceanic seamounts (MARANI & TRUA, 2002; MATTEI et alii, 2002; NICOLOSIet alii, 2006). The rapid migration of the trench, indicated by the progressive shifting of foredeep basins, and the huge block rotations oc-curring during Miocene to Quaternary, were re-sponsible for the development of the arcuate shape of the Calabrian Arc. Presently, despite active seis-micity in the slab, there is no clear evidence of sig-nificant back-arc extension and foredeep migration in the Calabrian Arc, leaving the question on whether the trench retreat process is active or not still open.
In the following sections we describe more in de-tail the main characters of the Italian back-arc basins and of the Sicily Channel, located in the African lower plate, which provides fundamental constraints to the understanding of the origin and evolution of volcanic seamounts in Italy.
2. -THE LIGURIAN-PROVENÇAL BASIN The early forming back-arc basin in Central Mediterranean is the Ligurian-Provençal basin, a tri-angular sea located between the Provençal-Catalan coast and the Corsica-Sardinia block, which opened during Oligo-Miocene times (fig. 1) (BURRUS, 1984; GORINI et alii, 1993). Extensional processes in the Ligurian-Provençal basin developed at the back of a north-west dipping subducting lithosphere, as at-tested by the presence of a volcanic arc erupting along the Sardinia and Provençal margins. Rifting es-tablished within a Variscan continental crust, except in the Gulf of Lions that was previously affected by Pyrenean thrusting. The Ligurian-Provençal basin is characterized by symmetric conjugate margins in term of crustal velocity structure (GAILLER et alii, 2009). From the Gulf of Lions and west Sardinia continental margins it is possible to recognize: 1) a thinned continental crust with a crustal thickness of 18 to 10 km; 2) a transitional zone where high lower crustal velocities, non-typical of continental or nor-mal oceanic crust, might correspond to lower crustal material or a mixture of serpentinised upper mantle
material with lower crustal material; and 3) an oceanic crust, 4 to 5 km thick, with typical vertical velocity gradients and relative velocity ranges. The anomalous thin oceanic crust has been related to the influence of a cool slab in back-arc basin, with the final breakup occurring close to the Sardinia side, as a consequence of the smaller crustal thickness on this margin (GAILLERet alii, 2009). In this area the existence of mid-oceanic ridge has been proposed based on this geometry and the pattern of magnetic
anomalies (BURRUS, 1984), despite the characteristic of a spreading ridge relief has not been observed on deep seismic profiles (DE VOOGD et alii, 1991). These three regions, which have been recognized on both margin sides, are wide and smooth along the Gulf of Lions margin, and narrow and steep along its conjugate Sardinia side.
The age of rifting has been deduced by syn-rift deposits, located along the western Sardinian and Provençal margins, which range from Oligocene (30
Fig. 1 - Map of volcanic islands and submerged seamounts, grouped by colour into 7 volcanic Sectors. Activity range is reported for each volcanic structure. On shore volcanoes are also reported on map.
- Mappa delle isole e delle strutture sommerse vulcaniche, raggruppate per colore in 7 Settori. Per ogni edificio vulcanico è riportato il periodo di attività. Sono riportati sulla mappa anche
- 28 Ma) to Aquitanian (21.5 Ma) (CRAVATTEet alii, 1974; CHERCHI & MONTADERT, 1982, SÉRANNE, 1999; GORINIet alii, 1993). Since the late Aquitanian post-rift deposits unconformably overlie the syn-rift sequence in Sardinia and in the Gulf of Lion. The transition between syn-rift and post-rift deposits also marks the starting of oceanic crust formation in the Ligurian-Provençal basin and the counterclockwise rotation and drifting of the Corsica-Sardinia block. The oceanic crust in the Ligurian-Provençal basin has not been drilled or sampled, and no data are available to constrain the termination of the oceanic spreading, which can be, however, constrained by the end of the counterclockwise rotation of the Cor-sica-Sardinia block. Paleomagnetic and geochrono-logical data indicate that the Corsica-Sardinia block rotated counterclockwise of ~45° after ~20.5 Ma, which can be regarded as the minimum rotation oc-curring during the Corsica-Sardinia drift, since an ad-ditional rotation may have taken place between the end of rifting (~21.5 Ma) and 20.5 Ma. On the other side, paleomagnetic results suggest that the rotation was virtually complete by 15 Ma (GATTACCECAet alii, 2007). Paleomagnetic results, geological correlations between Sardinia-Corsica and Provence together with oceanic crust extension defined by tectonic subsidence analysis (PASQUALEet alii, 1995) and com-patible with the constraints on Moho depth obtained from 3D gravity inversion (OGGIANO et alii, 1995) suggest that, before drifting, the Corsica-Sardinia block was located at the south of the Provençal mar-gin. In this scenario, the total opening amount of the southern part of the Ligurian-Provençal basin is ∼400 km during the drift. Between 20.5 Ma and 18 Ma, with a rotation pole located in the Ligurian Sea (around 43.5°N, 9.5°E), the average rate for the basin opening reached 9 cm yr−1 for the southern
part of the basin (GATTACCECAet alii, 2007).
3. - THE TYRRHENIAN SEA BASIN
During the Lower-Middle Miocene, extension mi-grated from the Ligurian-Provençal basin to the Tyrrhenian Basin, from Variscan to thickened Alpine crust presently outcropping in Calabria, Alpine Cor-sica and western Tuscany (JOLIVETet alii, 1997). The Northern Tyrrhenian Sea back-arc basin (fig. 1) de-veloped during the Neogene and Quaternary on the top of an active, western dipping, subducting slab, as evidenced today by the occurrence of intermediate seismicity and imaged by seismic tomography (SELVAGGI & CHIARABBA, 1995; PIROMALLO & MORELLI, 2003). Extensional tectonics continuously followed by compressive deformation responsible for the built up of the Apennine chain.
Both extensional and compressional tectonics progressively migrated from the western Tyrrhenian region toward the Apulia foreland, as demonstrated by the age of extensional and foredeep sedimentary basins, which become younger from the Tyrrhenian Sea toward the Adriatic foreland (e.g., ROYDENet alii, 1987; PATACCAet alii, 1992; CIPOLLARI& COSENTINO, 1995; FACCENNA et alii, 1997; JOLIVET et alii, 1998; COLLETTINIet alii, 2006). Extensional tectonics and crustal thinning in the Northern Tyrrhenian basin are marked by a system of spaced crustal shear zones, sedimentary basins and magmatic activity which gets younger toward the east from Corsica to the Apen-nine chain. In the westernmost Northern Tyrrhenian Sea (Pianosa island and Corsica) the sedimentary sequences which infill extensional sedimentary basins are Oligocene - Lower Miocene in age and are bounded by N-S trending east-dipping normal faults (BARTOLE, 1995; MAUFFRETet alii, 1999; MOELLERet alii, 2013, 2014). On the other hand, the sedimentary sequences occurring in the Apennine region where extensional tectonics is presently active and most of the normal faults strike NW-SE, are Pleistocene in age. Both extensional basins and magmatic centres shifted eastwards away from the rift axis at an aver-age velocity of 1.5-2 cm yr-1. No oceanic crust has
been produced in the Northern Tyrrhenian Sea basin.
In the Southern Tyrrhenian Sea extensional processes have been more intense, and new oceanic crust formed during Messinian-Early Pleistocene (KASTENSet alii, 1988; SARTORI, 1990; NICOLOSIet alii, 2006). Seismic data, ODP Site 653 results, and struc-tural and stratigraphic data on the on-shore western Calabria suggest that extension progressively migrated toward southeast as a consequence of the Ionian slab roll-back. In this basin rifting started along the western margin of the Southern Tyrrhenian Sea (Sardinian margin) during Serravallian, and progres-sively migrated southeastward in the Vavilov (late Messinian - early Pliocene) and Marsili (late Pliocene - early Pleistocene) basins. The conjugate, drifted margin of Sardinia is the Calabrian block, where the syn-rift deposits are Serravallian in age (MATTEIet alii, 2002). The average velocity of extension is of the order of 5-6 cm yr-1.
Rifting and basin subsidence were followed by a drifting stage, with the emplacement of oceanic crust and of partially serpentinised peridotite representing exhumed mantle rocks (PRADA et alii, 2016). In the area comprised between the east Sardinia and the west Campania margins seismic data allow to recognize three basement domains with different velocity and velocity-derived density models corresponding to continental crust, oceanic crust, and exhumed mantle (PRADAet alii, 2014, 2015).
The first domain includes the thinned continental crust of Sardinia (~20 km to ~13 km thick) and the conjugate Campania margin. The second domain, corresponds to the Cornaglia Terrace and its conjugate Campania Terrace; the Cornaglia Terrace appears to be oceanic in nature, with back-arc oceanic setting affinity. The third domain, corresponding to the two triangular-shaped Magnaghi and Vavilov Basins, includes the deepest (~3600 m) region of the Central Tyrrhenian Sea. This is characterized by velocities-depth relation-ships and absence of Moho reflections in seismic records that suggest a basement made of mantle rocks. This region contains two large NNE-SSW elon-gated volcanoes, the Magnaghi (~1500 m high above seafloor) and Vavilov (~2100 m high above seafloor) and several smaller ridges with the same trend (fig. 1). The syn-tectonic sequence interpreted in the Mag-naghi and Vavilov basins by several authors is localised in few areas and contains Messinian to early-middle Pliocene sediments (FABBRI & CURZI, 1979; TRINCARDI& ZITELLINI, 1987; MASCLE& REHAULT, 1990; SARTORIet alii, 2004). Lava flows and basaltic breccias are found interbedded with early Pliocene sediments in the Vavilov volcano surroundings, re-vealing magmatic activity at the end or soon after the formation of this sub-basin (MASCLE & REHAULT, 1990). Seismic observations (PRADAet alii, 2014, 2015) and ODP site 651 (ROBINet alii, 1987; BECCALUVAet alii, 1990; BONATTIet alii, 1990) support a basement mainly made of exposed mantle rocks, locally in-truded by basaltic dikes and suggest that in this area the large seamounts (e.g., Vavilov) are underlain by 10-20 km wide, relatively low-velocity anomalies in-terpreted as magmatic bodies locally intruding the mantle.The Marsili sub-basin is a flat, deep (3,500 m in average), roughly elliptical abyssal plain covering ∼8000 km2, with a NW-SE- trending major axis (∼110
km). It is characterised by a Moho depth, measured from sea level, in the order of 11 km, with a thinned lithosphere of <30 km (SUHALDOC& PANZA, 1989; NICOLICH, 1989; SCARASCIAet alii, 1994) and a heat flow values that reach over 200 mW m-2(DELLAVEDOVAet
alii, 1984; MONGELLIet alii, 1991). Basement depth in Marsili basin is ∼4 km (KASTENS& MASCLE, 1990), giving an average basin crustal thickness of 7 km. The occurrence of magnetic anomaly stripes in the Mar-sili basin suggests the presence of oceanic spreading in this sector of the Southern Tyrrhenian Sea (MARANI& TRUA, 2002; NICOLOSIet alii, 2006).
4. - THE SICILY CHANNEL
The Sicily Channel rift, located between Sicily Island and Tunisia, lies in the lower plate of the Central Mediterranean subduction system, in the
foreland of the Apennine-Maghrebian thrust-and-fold belt. Three principal NW-trending tectonic troughs (Pantelleria, Malta, and Linosa graben) char-acterise the tectonic structure of the area, repre-senting morphological depressions with water depths ranging from 1,300 to more than 1,700 m, significantly deeper than the other Sicily Channel areas (400 m depths in average). The Pantelleria, Malta and Linosa tectonic depressions are controlled by NW-directed sub-vertical normal faults clearly observable in seismic lines (CIVILEet alii, 2010). The Sicily Channel rift system is filled by Lower Pliocene-Pleistocene turbidites characterized by thicknesses ranging between 1000 and 2000 m, whereas on the continental platform the Pliocene-Pleistocene sediments do not exceed a thickness of 500 m (MALDONADO& STANLEY, 1977).
Detailed seismo-stratigraphic analyses allow to reconstruct the entire tectonic history of the rifting (CIVILE et alii, 2010). In particular the pre-rift sequence is formed by undifferentiated Miocene deposits, corresponding to the Late Tortonian-Messinian Terravecchia Formation, that do not show fault-related thickness changes. The syn-rift sequence is represented by the Early Pliocene deposits (Trubi Formation), which show a growth wedge-shaped geometry and divergent fanning strata down the dip slope of the tilted fault-blocks. The post-rift succession, probably Late Pliocene-Quaternary in age, is characterized by sub-parallel reflectors that drape the morphology below (CIVILE
et alii, 2010). A wide N-S trending belt characterized by localized uplifts and depocentres, alkaline volcanics and structural inversions, separates the Pantelleria trough to the west from the Malta and Linosa troughs to the east. This belt presents evidence of strike-slip tectonics, acting as a transfer fault zone between two segments of the rift system (ARGNANI, 1990).
The Sicily Channel rifting occurred in two main deformation phases. The first phase (Late Messinian-Early Pliocene) was characterized by crustal stretch-ing and by the activity of NW-SE oriented normal faults that defined the main structure of the tectonic depressions. The second phase started during Late Pliocene-Pleistocene and was associated with a widespread increasing of volcanic activity.
5. - THE MAGMATISM
The Western Mediterranean is characterized by an intense volcanic activity since the Oligocene. This igneous activity accompanied the geodynamic evolution of the Africa-Eurasia convergence during the last 30 Ma (e.g., BECCALUVAet alii, 1985, 1990;
SAVELLI, 1988, 2002; CONTICELLI & PECCERILLO, 1992; DOGLIONIet alii, 1997; GUEGUENet alii, 1998; JOLIVET & FACCENNA, 2000; FACCENNA et alii, 2001b; CONTICELLIet alii, 2002, 2007, 2009a, 2010, 2015a; MATTEIet alii, 2004, 2010; PECCERILLO, 2003; PECCERILLO & LUSTRINO, 2005; PECCERILLO & MARTINOTTI, 2006; FRANCALANCI et alii, 2007; PECCERILLOet alii, 2008; ROSENBAUMet alii, 2008; AVANZINELLI et alii, 2009; ALAGNA et alii, 2010; LUSTRINO et alii, 2011; TOMMASINI et alii, 2011; CARMINATI et alii, 2012; AMMANNATIet alii, 2016; PECCERILLO, 2017). However, little is known about the submarine volcanism that has occurred during the last 30 Ma in the Central Mediterranean due to the paucity of samples and data available. The following description of petrologic, geochemical, and isotopic characteristics of off-shore sub-marine and sub-aerial volcanic rocks occurring in the Central Mediterranean regions is made using the large-data set from GEOROC (For reference see records # 3226, 3483, 3932, 4345, 4353, 4369, 4370, 4371, 4468, 4670, 4672, 4862, 4923, 5163, 5164, 5444, 6128, 6814, 6817, 7254, 7480, 7583, 7585, 7586, 7605, 7714 8248, 8259, 8262, 8272, 8426, 8435, 9231, 9239, 9453, 9457, 9478, 9495, 9534, 10248, 10267, 10391, 10938, 11090, 11126, 11285, 11614, 11690, 12014, 12466, 12525, 12526, 12849, 13094, 13219, 14161, 14189, 14347, 14349, 15106, 17980, 18207, 18328, 18349, 19028, and 19143 at http://georoc.mpch-mainz.gwdg.de/georoc/).
6. - LIGURIAN VOLCANIC SEAMOUNTS SECTOR
The volcanic fields of this area are located in the north-westernmost sector of the Central Mediterranean region (fig. 1). Volcanic rocks lie well within the eastern portion of the Ligurian-Provençal basin between the Ligurian Shoreline at north-west and the western shoreline of Corsica Island at south-east (fig. 1). The volcanic fields are all submarine and comprise the Spinola/Tristanite and the Calypso ridges, the Ulysse/Genova Gulf Central Volcano, the Occhiali/Doria and the Genova volcanoes (PENSAet alii, this volume ).
In this area the volcanic activity developed entirely during the Miocene, spanning from 20.6 to 7.3 Ma with emplacements of dikes, lava flows and few submarine ignimbrites (FANUCCI et alii, 1993; RÉHAULT et alii, 2012). Lithologies range from olivine-basalts and shoshonites to high-K basaltic andesites, trachyandesites, and high-K andesites (fig. 2). Petrological affinity ranges from alkaline (Cap Corse off-shore) to high-K calc-alkaline (Tristanite ridge) to shoshonitic (Monte
Doria, Genova Gulf Central Volcano) series (RÉHAULT et alii, 2012).
The patterns of incompatible trace element normalised to primordial mantle (fig. 3) show a clear orogenic affinity for the samples from the eastern sector of the Ligurian-Provençal basin. Geochemical and petrological characteristics of these off-shore volcanic rocks suggest they are closely related with the calc-alkaline volcanic rocks of the on-shore Ligurian magmatic field occurring in the Nice area, between Monaco, Antibes and Cannes (LUSTRINO et alii, 2017, and references therein). However, the off-shore volcanic rocks from the eastern sector of the Ligurian-Provençal basin are younger than those of the on-shore cropping out on the north-western margin of the basin, in the Nice surroundings, which date between 33 and 26 Ma (LUSTRINOet alii, 2017).
The evolution of the magmatism in this area and its eastward migration with time are related with the counterclockwise rotation of the Corsica-Sardinia block and the opening of the Ligurian-Provençal basin (e.g., ROLLETet alii, 2002; GATTACCECAet alii, 2007; OUDETet alii, 2010; RÉHAULTet alii, 2012).
Fig. 2 - Total Alkali Silica (LEMAITREet alii,2002) for the Mediterranean volcanic and seamount sectors. Source data are from GeoRoc (see text for more details). The inset shows the reference fields: 1 - Picro-basalt, 2 - Basalt, 3 - Basaltic andesite, 4 - Andesite, 5 - Dacite, 6 - Rhyolite, 7 - Trachy-basalt, 8 - Basaltic trachy-andesite, 9 - Trachy-andesite, 10 - Trachyte/trachydacite, 11 - Tephrite/Basanite, 12 - Phono-Tephrite, 13 - Tephri-Phonolite,
14 - Phonolite, 15 - Foidite.
- Diagramma Total Alkali vs. Silica (LEMAITREet alii, 2002) dei diversi settori di seamount vulcanici nell’area Mediterranea. Fonte dei dati: GeoRoc (maggiori dettagli sono contenuti nel testo). Nel riquadro sono riportati i campi di riferimento: 1- Picro-basalto, 2 - Basalto, 3 - Andesite basaltica, 4 - Andesite, 5 - Dacite, 6 - Riolite, 7 - Trachi-basalto, 8 - Trachi-andesite basaltica, 9 - Trachi-andesite, 10 - Trachite/Trachi-dacite,
7. - CORSICA-SARDINIAN VOLCANIC SEAMOUNTS SECTOR
The volcanic fields of this area are located on the eastern off-shore of the Corsica-Sardinia block, straddling the Corsica and Sardinia channels, two deep N-S morphological features that bound the western margin of the Tyrrhenian basin (MARANIet alii, 1993; MASCLEet alii, 2001) (fig. 1). In this sector, the volcanic rocks are found both as submarine centres with the Cornacya, Quirinus and Cornaglia volcanic seamounts, at south east of Sardinia Island (SELLI, 1985; MASCLEet alii, 2001; CARMINATIet alii, 2012), and in two cases emerged above the sea level at Capraia Island with the diachronous coa-lescent Capraia and Zenobito volcanoes (e.g., RODOLICO, 1938; FRANZINI, 1964; ALDIGHIERI et alii, 2004; CERRINA-FERRONI, 2003; CHELAZZI et alii, 2006; POLI& PECCERILLO, 2016; PECCERILLO, 2017).
In this area the volcanic activity developed mainly during the Miocene (12.6-7.1 Ma; BARBERI et alii, 1986; ALDIGHIERIet alii, 1998; MASCLE et alii, 2001; GASPARONet alii, 2009) with only one single volcanic event, the Zenobito monogenetic volcano, occurring in the lower Pliocene at 4.6 Ma. Volcanic products are mainly made up by dikes, lava flows, cinder cones, and ignimbrites (e.g., RODOLICO, 1938; FRANZINI, 1964; CERRINA-FERRONI, 2003; ALDIGHIERI et alii, 2004; CHELAZZIet alii, 2006; GAGNEVINet alii, 2007; CONTICELLIet alii, unpublished data). Rocks range in composition from high-K andesite to high-K rhyolites and trachytes passing through trachyan-desites, high-K dacites and latites (fig. 2). Petrological affinity ranges from high-K calc-alkaline (Capraia vol-cano) to shoshonitic (Cornacya) series. A transitional affinity from orogenic to within-plate is observed for the Zenobito scoria and lavas (PENSA et alii, this volume). The patterns of incompatible trace element normalised to primordial mantle (fig. 3) show a clear orogenic affinity for all samples, showing negative spikes at Ba, Ta, Nb, P, and Ti and positive at Th, U, and Pb, with the exception of the Zenobito volcanic rocks that show a transitional character with signifi-cant decrease of both positive and negative spikes. Geochemical and petrological characteristics of Miocene rocks suggest they are closely related with the ultrapotassic volcanic rocks found on-shore at Sisco (Corsica), which are older (14 Ma, CIVETTAet alii, 1978) than those of Capraia and Cornacya (BARBERI et alii, 1986; ALDIGHIERI et alii, 1998; MASCLE et alii, 2001; GASPARON et alii, 2009). A decrease in the potassic character with time and eastward may be explained with the eastward roll-back of the subduction (CONTICELLI et alii, 2007, 2009a, 2010, 2015a; PECCERILLO, 2017).
8. - ETRUSCAN VOLCANIC SEAMOUNTS SECTOR
This volcanic seamounts sector is located between the 42nd parallel N and Ponza Island (fig. 1, PENSA
et alii, this volume). The Etruschi and Tiberino seamounts are the northernmost volcanic seamounts, whilst at south, close to 41st parallel N, are located the Ponza and Palmarola volcanic islands, but sub-marine volcanic products are also found at Zannone Island and along the Tyrrhenian escarpment (e.g., DE RITAet alii, 2001; CONTE& DOLFI, 2002; CADOUXet alii, 2005; CONTEet alii, 2016; PECCERILLO, 2017).
No chronological and compositional data are available for the northernmost Etruschi and Tiberino seamounts, whereas several geochronological absolute ages are available for the southernmost volcanic rocks showing a wide time span of em-placement from Pliocene to Pleistocene (BARBERIet alii, 1967; SAVELLI, 1983; CADOUX et alii, 2005; CONTEet alii, 2016). At Ponza Island two different epochs of magmatism have been recognised: the oldest between 5.0 Ma and 3.1 Ma, which emplaced submarine rhyolitic hyaloclastites (although DERITA
et alii, 2001 suggested a younger age of 2.5 Ma based on stratigraphic considerations); the youngest with the emplacement of Monte La Guardia succession between 1.2 and 1.05 Ma. The Palmarola volcanic rocks have intermediate absolute ages (1.83-1.56 Ma) between the two Ponza Epochs, whilst those from Palmarola off-shore (4.01-3.86 Ma) overlap those of the oldest Ponza Epoch (PENSAet alii, this volume).
The oldest volcanic products at Ponza and Pal-marola islands are made up by high-silica domes and dykes, which are both mantled by high-silica hyalo-clastites (DERITAet alii, 2001; AUBOURGet alii, 2002). Sub-aerial lava flows, lapilli to scoriae fall and flow deposits are found along the Monte La Guardia volcanic succession of the youngest Ponza Island epoch. The early Ponza Island rocks are high-silica and fall within the field of high-K rhyolites (fig. 2), plotting well within the igneous rocks of the Tus-can Anatectic Province (CONTICELLI et alii, 2010). The young Ponza Island rocks belonging to the Monte La Guardia succession range in composi-tion from olivine-bearing trachytes to trachytes, with a transitional character from high-K to shoshonite series, which partially overlap the Torre Alfina lamproite-like olivine-latites in the K2O vs. silica diagram (authors’ unpublished data). Pal-marola Island rocks, on the other hand, range in composition from latites, through trachytes to high-K rhyolites, overlapping the field of coeval Tolfa, Manziana, and Cerite rocks (PINARELLI, 1987, 1991; BERTAGNINI et alii, 1995; CONTICELLI
The petrological affinity of Ponza and Palmarola islands rocks range from anatectic for the old Ponza Is-land epoch, rhyolites to shoshonitic for the Palmarola Island and some young Ponza Island rocks, with La Guardia rocks being alkaline ultrapotassic (authors’ un-published data). The patterns of incompatible trace el-ement normalised to primordial mantle (fig. 3) show
strong similarities with those of the San Vincenzo and Roccastrada anatectic rhyolites (e.g., FERRARA et alii, 1989; PINARELLIet alii, 1989; FELDSTEINet alii, 1994). On the other hand, the Palmarola Island rocks show patterns with a stronger negative spikes at Sr, Eu, Ti, and Ba than those on old Ponza Island, with smooth or no negative spike at Ta and Nb. The younger Monte
Fig. 3 - Spider diagrams (HOFMANN, 1997) for Mediterranean volcanic and seamount sectors, data are normalised to Primordial Mantle values of MCDONOUGH& SUN(1995). For all the sectors, except the Etruscan one, only data with MgO >3 % wt. were selected. Source data are from GeoRoc (see text for more details). For
the Aeolian - E Tyrrhenian and Sicily Channel Sectors the offshore activity is represented by star symbols.
- Distribuzione degli elementi incompatibili (HOFMANN, 1997) normalizzati al Mantello Primordiale (MCDONOUGH& SUN, 1995) dei diversi settori di seamount vulcanici nell’area Mediterranea. Per tutti i settori, ad eccezione di quello Etrusco, sono stati selezionati solo i dati con MgO >3% wt. Fonte dei dati: GeoRoc (maggiori dettagli sono contenuti nel testo).
La Guardia Ponza rocks show patterns of incom-patible trace element normalised to primordial man-tle (fig. 3) that are closely overlapping those of the Tuscan lamproite-like rocks (e.g., CONTICELLI, 1998; CONTICELLIet alii, 2007, 2009a, 2011, 2013, 2015 a,b).
9. - NEAPOLITAN VOLCANIC SEAMOUNTS SECTOR
These volcanic seamounts are distributed in the off-shore of the active Neapolitan volcanoes (i.e., AVANZINELLIet alii, 2009; CONTICELLI et alii, 2010, 2015a), and they are made up by the Ventotene and Santo Stefano Islands, La Botte, the Ventotene vol-canic Ridge, the Albatros/Cicerone seamounts, and the Ischia and Procida Islands (fig. 1, PENSAet alii, this volume). No data about Ventotene ridge and the Albatros/Cicerone seamount are available, although a large set of data is available for the Ventotene, Santo Stefano, Ischia, and Procida Islands (e.g., CRISCIet alii, 1989; POLIet alii, 1987, 1989; CIVETTA
et alii, 1991; D’ANTONIO & DI GIROLAMO, 1994; PIOCHIet alii, 1999; D’ANTONIOet alii, 1999, 2013; CONTICELLIet alii, 2004, 2007, 2010; DEASTISet alii, 2004; FEDELEet alii, 2006; AVANZINELLIet alii, 2007; BROWNet alii, 2014; MAZZEOet alii, 2014; MELLUSO
et alii, 2014; CASALINIet alii, 2017, 2018; PECCERILLO, 2017).
Ventotene along with Santo Stefano Islands are the sub-aerial remnants of a large collapsed strato-volcano with product erupted in a time span between 0.8 and 0.13 Ma (BARBERI et alii, 1967; FORNASERI, 1985; METRICHet alii, 1988). The Ischia Island is the sub-aerial remnant of a large subma-rine stratovolcano with the oldest outcropping vol-canic rocks dated at 0.15 Ma with volvol-canic activity that proceeded continuously until historical times (1320 AD)(e.g., CAPALDIet alii, 1976; GILLOTet alii, 1982; POLIet alii, 1987, 1989; ORSIet alii, 1996). The volcanic activity of Procida Island spans between 70 ka and 14 ka (e.g., D’ANTONIO & DI GIROLAMO, 1994; D’ANTONIOet alii, 1999; DEASTISet alii, 2004; FEDELEet alii, 2006).
The Ventotene Island volcanic rocks range in com-position from basalts to trachybasalts, shoshonites, latite trachy-phonolites and phonolites, whilst those from Santo Stefano Island are monotonously phonolites. Ischia Island volcanic rocks are known almost exclusively from sub-aerial outcrops (DE VITAet alii, 2010; SBRANA& TOCCACELI, 2011). They range in composition from (fig. 2) shoshonites, to latites and trachytes, with some rocks piercing the boundary with phonolites (e.g., CASALINIet alii, 2017, 2018, and references therein). Procida volcano is characterised by the least evolved products of the
entire Neapolitan off-shore sector, and at a larger scale, of the entire Neapolitan district of the Roman Magmatic Province (e.g., CONTICELLI et alii, 2004, 2010, 2015a; AVANZINELLIet alii, 2009). These rocks range in composition from potassic trachybasalts to shoshonites, latites and few trachytes (e.g., D’ANTONIO& DIGIROLAMO, 1994; DEASTISet alii, 2004; FEDELE et alii, 2006).
The petrological affinity of the rocks of the Neapolitan sector is shoshonitic (CONTICELLIet alii, 2010), with the most mafic ones showing patterns of incompatible trace element normalised to pri-mordial mantle (fig. 3) with orogenic signatures although with decreasing negative spikes at Ba, Ta, Nb, P, and Ti passing from Ventotene Island mafic rock to Procida and Ischia islands ones.
10. - CENTRAL TYRRHENIAN VOLCANIC SEAMOUNTS SECTOR
These volcanic seamounts belong to the central domain of the Tyrrhenian basin, which corresponds to the two triangular-shaped Magnaghi and Vavilov sub-basins. This is the deepest sector of the Central Tyrrhenian Sea, with volcanoes lying, in some cases, directly on a basement made of mantle rocks (PRADAet alii, 2016). Beside the large Magnaghi and Vavilov volcanic seamounts other minor volcanic seamounts occur, which are namely: Marco Polo, Columbus, Gortani, D’Ancona, Virgilio, Augusto, Quirra, and Livia seamounts, and Virgilio II lava field (fig. 1). In addition, in this sector of the Tyrrhenian Sea are also grouped the southernmost volcanic fields found at the western side of the Aeolian Islands (fig. 1), aligned almost E-W, which are namely: Creusa seamount, Ustica Island, Prometeo seamount, Aceste/Tiberio seamounts, Garibaldi/Glauco seamounts, Anchise seamount (fig. 1) (PENSAet alii, this volume).
Volcanic rocks from the Magnaghi and Vavilov sub-basins were erupted between 4.3 and 0.09 Ma (FERAUD, 1990; PECCERILLO, 2017), whereas vol-canic rocks from the E-W southernmost alignment have ages between 5.2 and 0.13 Ma (PENSA et alii,
this volume).
Geochemistry and petrological data of volcanic rocks from the deepest region of the Tyrrhenian seafloor are rare and in most cases samples are strongly altered. Nonetheless they range in compo-sition from basalts and hawaiites to mugearites, and trachyte (fig. 2), but some foiditic to basanitic sam-ples from Vavilov and Gortani seamounts are also found (e.g., DIETRICHet alii, 1977, 1978; BARBERIet alii, 1978; KASTENSet alii, 1988; KASTENS& MASCLE, 1990; BECCALUVA et alii, 1982, 1990; PECCERILLO,
2017). MORB-type rocks are from ODP site 655 and DSDP 373A, whilst OIB-type rocks were found in Vavilov, Magnaghi, Quirra, and Columbus seamounts, showing a roughly bell shaped pattern for incompatible trace elements when normalised to primordial mantle (fig. 3). An OIB-type petrological affinity is also found for volcanic rocks from Ustica Island, Aceste and Prometeo seamounts, among the off-shore Tyrrhenian volcanoes of the southern-most E-W alignment. The volcanic rocks of Anchise seamount, located between Ustica Island and Aceste seamount, have a clear orogenic signature with pat-terns showing negative spikes at Ta, Nb, and Ti.
11. - AEOLIAN - EASTERN TYRRHENIAN VOLCANIC SEAMOUNTS SECTOR
These volcanic seamounts and islands are found in the south-easternmost region of the Tyrrhenian Sea (fig. 1), and composed by the Aeolian Islands (e.g., Stromboli, Vulcano, Panarea, Lipari, Salina, Filicudi, and Alicudi) and the surrounding volcanic seamounts between them and Marsili and Palinuro seamounts (e.g., Glabro, Enotrio, Diamante, Alcione, Lametini, Strombolino I and Strombolino II and Capo Vaticano seamounts); other minor volcanic seamounts are represented by the western continua-tion of the volcanic arc (e.g., Eolo, Enarete, Sisisfo, and Tiro seamounts, PENSAet alii, this volume).
Volcanic rocks of this sector range in ages from 1.3-1.0 Ma (e.g., Marsili and Sisifo seamounts) to present time (e.g., BECCALUVA et alii, 1981a, 1985; SAVELLI, 1988; MARANI& TRUA, 2002; TRUAet alii, 2002; DE ROSA et alii, 2003; PECCERILLO, 2017), whilst the subaerial rocks of the Aeolian Islands range from 106 to 28 ka at Alicudi Island, from 250 to 30 ka at Filicudi Island, from 270 ka to 1220 AD at Lipari Island, from 155 to 8.7 ka at Panarea Island, from 250 to 16 ka at Salina Island, from 204 ka to present at Stromboli Island, and from 130 ka to 1890 AD at Vulcano (e.g., GILLOT & VILLARI, 1980; KELLER, 1980; GILLOT, 1987; GABBIANELLIet alii, 1990; PASQUARÉet alii, 1993; VOLTAGGIOet alii, 1997; DE ROSA et alii, 2003; FRANCALANCI et alii, 2004, 2007, 2013; TOMMASINIet alii, 2007; LÉOCAT, 2010; WIJBRANS et alii, 2011; LUCCHI et alii, 2013; PECCERILLO, 2017).
The volcanic rocks from this sector of the Tyrrhenian Sea range in composition from basalts to basaltic andesite, andesite, dacite, and rhyolites (fig. 2), but a shoshonitic to slightly potassic series can also be found with rocks ranging from K-trachybasalts, to shoshonite, latite, and trachyte (e.g., KELLER, 1980; BECCALUVA et alii, 1981a, 1985; FRANCALANCI et alii, 1988, 1989, 1993, 2004, 2007,
2013; MARANI& TRUA, 2002; TRUAet alii, 2002; DE ROSAet alii, 2003; TOMMASINIet alii, 2007; LUCCHIet alii, 2013; PECCERILLO, 2017 and references therein). Petrological affinity of volcanic products is orogenic with patterns of incompatible trace elements normalised to primordial mantle showing strong negative spikes at Ta, Nb, P, Zr, and Ti, and positive at Pb (fig. 3).
12. - SICILY CHANNEL VOLCANIC SEAMOUNTS SECTOR
These volcanic seamounts are located in the Sicily Channel and include the Pantelleria and Linosa Is-lands. They are composed by Tetide, Anfitrite, Galatea, Euridice, and Empedocle seamounts (i.e., Ferdinandea/Graham, Terrible, Nerita seamounts), along with Nameless, Linosa II and Alfil/Linosa III volcanic seamounts (fig. 1, PENSAet alii, this volume). Volcanic rocks of this sector range in ages from 1.06 Ma to 1891 AD (e.g., CORNETTE et alii, 1983; SAVELLI, 2001; PECCERILLO, 2017; LODOLO et alii, 2017) although a much older K-Ar age of 9.6 Ma was found for the Nameless seamount (BECCALUVA
et alii, 1981b).
The volcanic rocks of the volcanoes of the Sicily Channel are invariably mildly Na-alkaline (e.g., VILLARI, 1974; BECCALUVAet alii, 1981b; CALANCHI
et alii, 1989; MAHOOD& STIMAC, 1990; ESPERANÇA & CRISCI, 1995; CIVETTA et alii, 1998; BINDIet alii, 2002; AVANZINELLIet alii, 2004, 2014; CONTICELLI
et alii, 2004; ROTOLO et alii, 2006; DIBELLA et alii, 2008; DICARLOet alii, 2010; COLTELLIet alii, 2016; PECCERILLO, 2017), ranging in composition from basalts and hawaiites to mugearite, benmoreite, trachytes (comenditic and pantelleritic), pantellerites and in some cases comendites (fig. 3, PENSA et alii, this volume).
The petrological affinity of the off-shore volcanic rocks of the Sicily Channel is anorogenic, rift-related, with typical bell shaped patterns of incom-patible trace elements normalised to primordial mantle showing small negative spikes at Th, K, and Pb (fig. 3).
13. - SR-ND-PB ISOTOPES
Central Mediterranean volcanic rocks range from shoshonites, high-K calc-alkaline and calc-alkaline igneous rocks, which are followed lately by anoro-genic Na-alkaline within-plate rocks. As a whole, they have extremely variable radiogenic isotope com-positions (figs. 4, 5), displaying a geographic variation firstly from west to east and later from northwest to
southwest (see CONTICELLI et alii, 2007, 2010; PECCERILLOet alii, 2017 and references therein).
The observed isotope variation covers almost the entire spectrum of mantle and upper crust values, complicating the interpretation of the petrogenetic grid of the Central Mediterranean volcanism (e.g., HAWKESWORTH & VOLLMER, 1979; VOLLMER & HAWKESWORTH, 1981; VOLLMER, 1989; CONTICELLI
et alii, 2002, 2004, 2007, 2009a,b, 2010, 2011, 2013, 2015a,b; GASPERINIet alii, 2002; BELL et alii, 2004; PECCERILLO, 2003, 2017; AVANZINELLI et alii, 2009, 2012, 2014; ALAGNAet alii, 2010).
143Nd/144
Ndi vs. 87Sr/86
Sri (fig. 4) values anticor-relate overlapping both the MORB field (e.g., Sicily Channel, Central Tyrrhenian, Aeolian - E Tyrrhenian sectors) and the fields of the Italian ultrapotassic, shoshonitic and calc-alkaline Pliocene-Pleistocene volcanic rocks (Aeolian - E Tyrrhenian, Neapolitan, Etruscan, and Corsica - Sardinian sectors). No iso-topic data are available for the Ligurian sector.
The same geographic variation can be observed in the diagrams where Pb isotopes are plotted (fig. 5). The Central Mediterranean off-shore volcanic rocks, analogously to what observed for the Pliocene-Pleis-tocene on-shore volcanic rocks along the Tyrrhenian border of the Italian peninsula, fill the gap between upper crustal composition and FOZO (HARTet alii, 1992) passing through the isotopic composition of EM II end-member (ZINDLER& HART, 1986), which is believed to represent a recycled sedimentary com-ponent. On the other hand, Central Tyrrhenian Sea volcanic rocks of the Magnaghi and Vavilov sub-basins have a clear MORB-type signature, with those from the Neapolitan volcanic sector (Ventotene and Ischia volcanoes) characterised by a trend departing from the general Roman array, pointing to the Central Tyrrhenian MORB (fig. 5). FOZO isotope composi-tions are only approached by volcanic rocks from magmatic suites south of the 41st parallel. A less-depleted asthenospheric mantle source has been
Fig. 4 - Plot of 143Nd/144Nd vs. 87Sr/86Sr for Mediterranean volcanic seamount sectors. Source data are from GeoRoc (see text for more details). Reference
fields are also reported: MORBs are from STRACKEet alii(2003), Q: La Queglia, PN: Pietre Nere, RMP: Roman Magmatic Province, TMP: Tuscan Magmatic Province, LuMP: Lucanian Magmatic Province and Italian sediments are from CONTICELLIet alii (2015a). For the Aeolian - E Tyrrhenian and Sicily Channel
Sectors the offshore activity is represented by star symbols. Isotopic data for the Ligurian Sector not available in literature.
- Correlazione tra 143Nd/144Nd e 87Sr/86Sr dei prodotti appartenenti ai diversi settori di seamount vulcanici nell’area Mediterranea. Fonte dei dati: GeoRoc (maggiori dettagli sono
contenuti nel testo). Sono riportati alcuni campi per riferimento: MORB da STRACKEet alii (2003), Q: La Queglia, PN: Pietre Nere, RMP: Provincia Magmatica Romana, TMP:
Provincia Magmatica Toscana, LuMP: Provincia Magmatica Lucana e sedimenti italiani da CONTICELLIet alii (2015a). L’attività offshore dei Settori Eoliano - E Tirrenico e del Canale di Sicilia è rappresentata da simboli a stella. I dati di composizione isotopica per il Settore Ligure non sono reperibili in letteratura.
Fig. 5 - Plots of 87Sr/86Sr (a.), 143Nd/144Nd (b.) and 208Pb/204Pb (c.) vs. 206Pb/204Pb for Mediterranean volcanic seamount sectors. Source data are from
Geo-Roc (see text for more details). Reference fields are also reported: MORBs are from STRACKEet alii(2003), Q: La Queglia, PN: Pietre Nere, RMP: Roman Magmatic Province, TMP: Tuscan Magmatic Province and LuMP: Lucanian Magmatic Province are from CONTICELLIet alii(2015a). For the Aeolian - E Tyr-rhenian and Sicily Channel Sectors the offshore activity is represented by star symbols. Isotopic data for the Ligurian Sector not available in literature. - Correlazione tra 87Sr/86Sr (a.), 143Nd/144Nd (b.) e 208Pb/204Pb (c.) vs. 206Pb/204Pb dei prodotti appartenenti ai diversi settori di seamount vulcanici nell’area Mediterranea. Fonte
dei dati: GeoRoc (maggiori dettagli sono contenuti nel testo). Sono riportati alcuni campi per riferimento: MORB da STRACKEet alii (2003), Q: La Queglia, PN: Pietre Nere, RMP:
Provincia Magmatica Romana, TMP: Provincia Magmatica Toscana, LuMP: Provincia Magmatica Lucana da CONTICELLIet alii (2015a). L’attività offshore dei Settori Eoliano - E Tirrenico e del Canale di Sicilia è rappresentata da simboli a stella. I dati di composizione isotopica per il Settore Ligure non sono reperibili in letteratura.
proposed for the southernmost sector of Italian magmatism (e.g., BECCALUVA et alii, 1981a; AVANZINELLIet alii, 2009). Similar isotopic compo-sitions are also reported for calc-alkaline rocks from the Aeolian Arc (e.g., FRANCALANCI et alii, 1993, 2007; PECCERILLO, 2001, 2005; TOMMASINIet alii, 2007).
14. - GENESIS OF MAGMATISM AND GEODYNAMIC OUTLINES
The origin of Pliocene-Pleistocene Central Me-diterranean volcanic rocks have been the subject of a scientific debate focused on two main possible mechanisms: a) within-plate origin, possibly linked to partial melting of an up-rising mantle plume (e.g., VOLLMER& HAWKESWORTH, 1980; VOLLMER, 1990; AYUSOet alii, 1998; CASTORINAet alii, 2000; GASPERINI
et alii, 2002; BELLet alii, 2004); b) orogenic to post-orogenic origin, related to partial melting of the sub-continental lithospheric metasomatised mantle at a destructive plate margin, with important con-tributions from recycled sediments (e.g., COXet alii, 1976; PECCERILLO, 1985, 2005; ROGERS et alii, 1986; BECCALUVA et alii, 1981a; CONTICELLI & PECCERILLO, 1992; DOWNES et alii, 2002; BIANCHINIet alii, 2008).
Some of the authors suggesting the within-plate origin also pointed out the need for an increasing influence of an upper crustal geochemical component northward, although no convincing reasons have been provided to explain it in the frame of a within-plate, extensional geodynamic setting (e.g., HAWKESWORTH& VOLLMER, 1979; VOLLMER, 1990; GASPERINI et alii, 2002; BELLet alii, 2004). On the other hand, there is an increasing consensus that calc-alkaline to shoshonitic and ultrapotassic rocks of Central Mediterranean are subduction-related magmas, generated through partial melting of a metasomatised upper mantle (e.g., CONTICELLI& PECCERILLO, 1992; CONTICELLI, 1998; CONTICELLI
et alii, 2002, 2004, 2007, 2010, 2015a; PECCERILLO, 2003, 2005, 2017; AVANZINELLI et alii, 2009; LUSTRINOet alii, 2011). The same holds true for the calc-alkaline to shoshonitic volcanic rocks of the Southern Tyrrhenian Sea of the Aeolian Arc and surrounding seamounts (e.g., FRANCALANCI et alii, 1993, 2007; PECCERILLO, 2003, 2005, 2017; TOMMASINI et alii, 2007; ALAGNA et alii, 2010), and of the Ligurian and Corsica sectors (e.g., CONTICELLI
et alii, 2002, 2010, 2015a; CHELAZZI et alii, 2006; PECCERILLO, 2003, 2017; LUSTRINO et alii, 2011; RÉHAULT et alii, 2012). The orogenic magmatism migrated following the Benioff plane retreat, in eastward direction first, and later south-eastwards.
Within plate magmas appeared in the back-arc basins 2-3 Ma after of end of orogenic igneous
activity (e.g., SAVELLI, 2002; LUSTRINOet alii, 2011; PECCERILLO, 2017). In addition, the opening of the Tyrrhenian back arc basin led to the emplacement of a MORB-type oceanic crust in the deepest region of the Tyrrhenian Sea, which was followed by the occurrence of within plate magmatism (e.g., SAVELLI, 2002; LUSTRINOet alii, 2011; PECCERILLO, 2017).
15. - CONCLUSIONS
The brief overview on the Tertiary-Quaternary geodynamic and magmatic evolution of the Central Mediterranean region provided in this contribution highlights the complexity of processes that this region has witnessed in the last 35 Ma, where the initial collision of Africa and Eurasia was followed by rapid retreat of the subducting slabs, their fragmentation and opening of back arc basins bordered by highly arcuate orogenic chains. Within this framework, magmatism shows a complexity of magma types that is rather unique and is still open to scientific de-bate. The knowledge of submarine volcanism is a key part of the picture and still far from complete, so that a comprehensive understating of the geody-namics of the Central Mediterranean will benefit im-mensely by future campaigns aimed at unravelling the seafloor volcanism.
Acknowledgements
Financial support was provided by PRIN 2015 funds (grant n. 2015EC9PJ5) to R.A., and 2015 (grant n. in-iziale: 20158A9CBM) to SC and MM.
REFERENCES
ALAGNA K. E., PECCERILLO A., MARTIN S. & DONATI C. (2010) - Tertiary to present evolution of
orogenic magmatism in Italy. Journal of the Virtual Explorer, 36: 1-63.
ALDIGHIERI B., GAMBA A., GROPPELLIG., MALARA G., PASQUARÉ G., TESTA B. & WIJBRANS J. (1998) -Methodology for the space-time definition of lateral collapse:
the evolution model of Capraia Island (Italy). In: BUCCIANTI A., NARDI G. & POTENZA R. (Eds), Proceedings of IAMG 1998, Isola di Ischia, Naples, 81-84.
ALDIGHIERI B., GROPPELLIG., NORINIG. & TESTA B. (2004) - Capraia Island: Morphology and Geology of
a Complex Volcanic activity during the Miocene and Pliocene. In: MORINI D. & BRUNI P. (Eds), The Regione Toscana project of Geological Mapping, case histories and data acquisition, Regione Toscana Government, Firenze, 51-59.
ALVAREZ W., COCOZZA T. & WEZEL F.C. (1974)
-Fragmentation of the Alpine orogenic belt by microplate dispersal. Nature, 248: 303-314.
AMMANNATIE., JACOBD.E., AVANZINELLIR., FOLEY S.F. & CONTICELLIS. (2016) - Low Ni olivine in
silica-undersaturated ultrapotassic igneous rocks as evidence for carbonate metasomatism in the mantle. Earth and Planetary Science Letters, 444: 64-74.
ANDERSONH. & JACKSONJ. (1987) - Active tectonics of
the Adriatic region. Geophysical Journal Royal As-tronomical Society, 91: 937-987.
ARGNANI A. (1990) - The Strait of Sicily rift zone:
foreland deformation related to the evolution of a back-arc basin. J. Geodyn. 12: 311-331.
AUBOURG C., GIORDANO G., MATTEI M. & SPERANZA F. (2002) - Magma flow in sub-aqueous
rhyolitic dikes inferred from magnetic fabric analysis (Ponza Island, W. Italy). Physics and Chemistry of the Earth, Parts A/B/C, 27(25-31), 1263-1272.
AVANZINELLI R., BINDI L., MENCHETTI S. & CONTICELLIS. (2004) - Crystallisation and genesis of
peralkaline magmas from Pantelleria Volcano, Italy: an integrated petrological and crystal-chemical study. Lithos,
73(1): 41-69.
AVANZINELLI R., BRASCHI E., MARCHIONNI S. & BINDI L. (2014) - Mantle melting in within-plate
continental settings: Sr-Nd-Pb and U-series isotope constraints in alkali basalts from the Sicily Channel (Pantelleria and Linosa Islands, Southern Italy). Lithos,
188: 113-129.
AVANZINELLI R., ELLIOTT T., TOMMASINI S. & CONTICELLIS. (2007) - Constraints on the genesis of
potassium-rich Italian volcanic rocks from U/Th disequilibrium. Journal of Petrology, 49(2): 195-223. AVANZINELLI R., LUSTRINO M., MATTEI M., MEL-LUSO L. & CONTICELLI S. (2009) - Potassic and
ultrapotassic magmatism in the circum-Tyrrhenian region: significance of carbonated pelitic vs. pelitic sediment recycling at destructive plate margins. Lithos, 113(1-2): 213-227. AYUSOR.A., DEVIVOB., ROLANDIG., SEALR.R. II & PAONE A. (1998) - Geochemical and isotopic
(Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from Vesuvius, Italy. J. Volcanol. Geoth. Res.
82: 53-78.
BARBERIF., BIZOUARDH., CAPALDIG., FERRARAG., GASPARINIP., INNOCENTIF., JORONJ.L., LAMBRET B., TREUIM. & ALLEGREC. (1978) - Age and nature
of basalts from the Tyrrhenian abyssal plain.Initial Re-ports of the DSDP, 42: 509-514.
BARBERIF., BORSIS., FERRARA G. & INNOCENTI F. (1967) - Contributo alla conoscenza vulcanologica e
mag-matologica delle Isole dell’Archipelago Pontino. Mem. Soc. Geol. Ital. 6: 581-606.
BARBERI F., FERRARA G., FRANCHI F., SERRI G., TONARINIS. & TREUILM. (1986) - Geochemistry and
geochronology of the Capraia Island volcanic Complex (North Tyrrhenian Sea, Italy). Terra Cognita 6: 185. BARBERIF., GASPARINIP., INNOCENTI F. & VILLARI
L. (1973) - Volcanism of the southern Tyrrhenian Sea
and its geodynamic implications. Journal of Geophysi-cal Research, 78: 5221-5232.
BARTOLE R. (1995) - The North Tyrrhenian-Northern
Apennines post-collisional system: constraints for a geody-namic model. Terra Nova, 7: 7-30.
BECCALUVAL., BONATTIE., DUPUYC., FERRARAG., INNOCENTI F., LUCCHINI F., MACERA P., PETRINI R., ROSSIP.L., SERRI G., SEYLER M. & SIENA F. (1990) - Geochemistry and mineralogy of volcanic rocks
from ODP sites 650, 651, 655 and 654 in the Tyrrhenian Sea. In: Proceedings of the Ocean Drilling Program, Scientific Results, 107: 49-74. Col-lege Station, TX (Ocean Drilling Program).
BECCALUVA L., COLANTONI P., SAVELLI C. & DI GIROLAMOP. (1981b) - Upper-Miocene submarine
vol-canism in the Strait of Sicily (Banco senza Nome). Bul-letin Volcanologique, 44(3): 573-581.
BECCALUVAL., COLTORTIM., PREMTII., SACCANIE., SIENAF.T. & ZEDAO. (1994) - Mid-ocean ridge and
suprasubduction affinities in the ophilitic belts from Albania. Ofioliti, 19: 77-96.
BECCALUVAL., GABBIANELLIG., LUCCHINIF., ROSSI P.L. & SAVELLIC. (1985) - Petrology and K/Ar ages of
volcanics dredged from the Eolian seamounts: implications for geodynamic evolution of the southern Tyrrhenian basin. Earth and Planetary Science Letters, 74: 2-3, 187-208. BECCALUVAL., GABBIANELLIG., LUCCHINIF., ROSSI
P. L., SAVELLI C. & ZEDA O. (1981a) - Magmatic
character and K/Ar ages of volcanics dredged from the Eolian seamounts (Tyrrhenian Sea). In: F.C. WEZEL (Ed.), Sedimentary Basins of Mediterranean Mar-gins, 361-368. Tecnoprint Bologna.
BECCALUVA L., ROSSI P.L. & SERRI G. (1982)
-Neogene to Recent volcanism of the southern Tyrrhenian-Sicilian area: Implications for the geodynamic evolution of the Calabrian arc. Earth Evol. Sci, 3: 222-238. BELL K., CASTORINAF., LAVECCHIA G., ROSATELLI
G. & STOPPAF. (2004) - Is there a mantle plume beneath
Italy?EOS 85: 541-547.
BERTAGNINI A., DE RITA D. & LANDI P. (1995)
-Mafic inclusions in the silica-rich rocks of the Tolfa-Ceriti-Manziana volcanic district (Tuscan Province, Central Italy): chemistry and mineralogy. Mineralogy and Petrology, 54(3-4): 261-276.
BIANCHINI G., BECCALUVA L. & SIENAF. (2008)
-Post-collisional and intraplate Cenozoic volcanism in the rifted Apennines/Adriatic domain. Lithos 101: 125-140.
BINDI L., TASSELLI F., OLMI F., PECCERILLOA. & MENCHETTI S. (2002) - Crystal chemistry of
clinopyroxenes from Linosa Volcano, Sicily Channel, Italy: implications for modelling the magmatic plumbing system.
BOCCALETTIM. & GUAZZONE G. (1974) - Remnant
arcs and marginal basins in the Cainozoic development of the Mediterranean. Nature, 252: 18-21.
BONATTIE., SEYLERM., CHANNELLJ., GIRARDEAU J. & MASCLE G. (1990) - Peridotites drilled from the
Tyrrhenian Sea, ODP LEG 107. In Proc. Ocean Drill. Program Sci. Results, 107: 37-47.
BROWNR.J., CIVETTAL., ARIENZO I., D’ANTONIO M., MORETTI R., ORSI G., TOMLINSON E.L., ALBERTP.G. & MENZIESM.A. (2014) - Geochemical
and isotopic insights into the assembly, evolution and dis-ruption of a magmatic plumbing system before and after a cataclysmic caldera-collapse eruption at Ischia volcano (Italy). Contributions to Mineralogy and Petrology,
168(3): 1035.
BURRUSJ. (1984) - Contribution to a geodynamic synthesis
of the Provençal Basin (North-Western Mediterranean). Marine Geology, 55: 247-269.
CADOUX A., PINTI D.L., AZNAR C., CHIESA S. & GILLOTP.Y. (2005) - New chronological and geochemical
constraints on the genesis and geological evolution of Ponza and Palmarola Volcanic Islands (Tyrrhenian Sea, Italy). Lithos,
81: 121-151, doi: 10.1016/j.lithos.2004.09.020.
CALANCHIN., COLANTONIP., ROSSIP.L., SAITTAM. & SERRIG. (1989) - The Strait of Sicily continental rift
systems: physiography and petrochemistry of the submarine volcanic centres. Marine Geology, 87(1): 55-83. CAPALDIG., GASPARINIP. & CIVETTAL. (1976) - The
geochronology and the volcanic history of the Ischia Island (Southern Italy)(No. INIS-MF-3149).
CARMINATIE., LUSTRINOM. & DOGLIONIC. (2012) - Geodynamic evolution of the central and western
Mediter-ranean: Tectonics vs. igneous petrology constraints. Tecto-nophysics, 579: 173-192.
CASALINIM., AVANZINELLIR., HEUMANNA., DEVITA S., SANSIVERO F., CONTICELLI S. & TOMMASINI S. (2017) - Geochemical and radiogenic isotope probes of
Is-chia volcano, Southern Italy: Constraints on magma cham-ber dynamics and residence time. American Mineralogist, 102(2): 262-274.
CASALINI M., HEUMANN A., MARCHIONNI S., CONTICELLI S., AVANZINELLI R. & TOMMASINIS. (2018) - Inverse modelling to unravel the radiogenic isotope
signature of mantle sources from evolved magmas: the case-study of Ischia volcano. Italian Journal of Geo-sciences, 137(3): 420-432.
CASTORINA F., STOPPA F., CUNDARI A. & BARBIERI M. (2000) - An enriched mantle source for Italy’s
melili-tite-carbonatite association as inferred by its Nd-Sr isotope signature. Mineral. Mag. 64: 625-639.
CERRINA-FERRONI A. (2003) - Sezioni: CAP100,
CAP110, CAP140, CAP150. In: Carta Geologica
della Toscana, Scala 1:10000,
http://159.213.57.101/geologia/Sezioni_zip_ra-ster/CAP150.zip.
CHELAZZI L., BINDI L., OLMI F., PECCERILLO A., MENCHETTI S. & CONTICELLI S. (2006)-
Lamproitic components in the high-K calc-alkaline volcanic rocks of the Capraia Island, Tuscan Magmatic Province: evidence from clinopyroxene crystal chemical data. Periodico di Mineralogia, 75: 75-94.
CHERCHIA. & MONTADERTL. (1982) - Oligo-Miocene
rift of Sardinia and the early history of the western Mediterranean basin. Nature, 298(5876): 736. CIFELLIF., MATTEIM. & DELLASETA M. (2008)
-Calabrian Arc oroclinal bending: The role of subduction. Tectonics, 27, TC5001.
CIFELLIF., MATTEI M. & ROSSETTI F. (2007) -
Tec-tonic evolution of arcuate mountain belts on top of a re-treating subduction slab: The example of the Calabrian Arc. Journal Geophysical Research, 112, B09101. CIPOLLARIP. & COSENTINO D. (1995) - Miocene
un-conformities in the Central Apennines: geodynamic signifi-cance and sedimentary basin evolution. Tectonophysics,
252: 375-389.
CIVETTA L., D’ANTONIO M., ORSI G. & TILTON G.R. (1998) - The geochemistry of volcanic rocks from
Pantel-leria Island, Sicily Channel: petrogenesis and characteris-tics of the mantle source region.Journal of Petrology,
39(8): 1453-1491.
CIVETTAL., GALLOG. & ORSIG. (1991) - Sr-and
Nd-isotope and trace-element constraints on the chemical evolu-tion of the magmatic system of Ischia (Italy) in the last 55 ka. Journal of Volcanology and Geothermal Re-search, 46(3-4): 213-230.
CIVETTA L., ORSI G., SCANDONE P. & PECE R. (1978) - Eastwards migration of the Tuscan anatectic
magmatism due to anticlockwise rotation of the Apennines. Nature, 276 (5688): 604-606.
CIVILED., LODOLOE. ACCETTELLAD., GELETTIE., BEN-AVRAHAM Z., DEPONTE D., FACCHIN L., RAMELLA L. & ROMEOR. (2010) - The Pantelleria
graben (Sicily Channel, Central Mediterranean): An ex-ample of intraplate ‘passive’ rift.Tectonophysics, 490: 173-183.
COLLETTINIC., DEPAOLAN. HOLDSWORTHH.R. & BARCHIM. (2006) - The development and behaviour of
low-angle normal faults during Cenozoic asymmetric ex-tension in the Northern Apennines, Italy. Journal of Structural Geology, 28: 333-352.
COLTELLIM., CAVALLAROD., D’ANNAG., D’ALESSANDRO A., GRASSAF., MANGANOG., PATANÈD. & GRESTA S. (2016) - Exploring the submarine Graham Bank in the
Sicily Channel. Annals of Geopysyscs.
CONTE A.M. & DOLFI D. (2002) - Petrological and
geochemical characteristics of Plio-Pleistocene Volcanics from Ponza Island (Tyrrhenian Sea, Italy). Mineralogy
CONTEA.M., PERINELLIC., BIANCHINI G., NATALI C., MARTORELLIE. & CHIOCCIF.L. (2016) - New
insights on the petrology of submarine volcanics from the Western Pontine Archipelago (Tyrrhenian Sea, Italy). Journal of Volcanology and Geothermal Research,
327: 223-239.
CONTICELLIS. (1998) - The effect of crustal
contamina-tion on ultrapotassic magmas with lamproitic affinity: min-eralogical, geochemical and isotope data from the Torre Alfina lavas and xenoliths, Central Italy. Chemical Geology, 149(1): 51-81.
CONTICELLIS., AVANZINELLI R., AMMANNATIE. & CASALINIM. (2015a) - The role of carbon from recycled
sediments in the origin of ultrapotassic igneous rocks in the Central Mediterranean.Lithos, 232: 174-196.
CONTICELLI S., AVANZINELLI R., MARCHIONNI S., TOMMASINIS. & MELLUSOL. (2011) - Sr-Nd-Pb
iso-topes from the Radicofani Volcano, Central Italy: con-straints on heterogeneities in a veined mantle responsible for the shift from ultrapotassic shoshonite to basaltic andesite magmas in a post-collisional setting. Mineralogy and Pe-trology, 103(1-4): 123-148.
CONTICELLI S., AVANZINELLIR., POLI G., BRASCHI E. & GIORDANOG. (2013) - Shift from lamproite-like
to leucititic rocks: Sr-Nd-Pb isotope data from the Monte Cimino volcanic complex vs. the Vico stratovolcano, Cen-tral Italy. Chemical Geology, 353: 246-266.
CONTICELLIS., BOARIE., BURLAMACCHIL., CIFELLI F., MOSCARDIF., LAURENZIM.A., PEDRAGLIOL.F., FRANCALANCIL., BENVENUTIM.G., BRASCHIE. & MANETTIP. (2015b) - Geochemistry and Sr-Nd-Pb
iso-topes of Monte Amiata Volcano, Central Italy: evidence for magma mixing between high-K calc-alkaline and leucititic mantle-derived magmas. Italian Journal of Geo-sciences, 134(2): 266-290.
CONTICELLIS., CARLSONR.W., WIDOME. & SERRI G. (2007) - Chemical and isotopic composition (Os, Pb,
Nd, and Sr) of Neogene to Quaternary calc-alkalic, shoshonitic, and ultrapotassic mafic rocks from the Italian peninsula: Inferences on the nature of their mantle sources.
In: BECCALUVA L., BIANCHINI G. & WILSON M. (Eds):Cenozoic Volcanism in the Mediterranean Area,
Geological Society of America, Special Paper,
418: 171-202.
CONTICELLI S., D’ANTONIO M., PINARELLI L. & CIVETTAL. (2002) - Source contamination and mantle
heterogeneity in the genesis of Italian potassic and ultra-potassic volcanic Rocks: Sr-Nd-Pb Isotope data from Roman Province and Southern Tuscany. Mineralogy and Petrology, 74: 189-222.
CONTICELLI S., GUARNIERI L., FARINELLI A., MATTEIM., AVANZINELLIR., BIANCHINIG., BOARI E., TOMMASINI S., TIEPOLO M., PRELEVIĆ D. & VENTURELLIG. (2009a) - Trace elements and
Sr-Nd-Pb isotopes of K-rich, shoshonitic, and calc-alkaline mag-matism of the Western Mediterranean Region: genesis of
ultrapotassic to calc-alkaline magmatic associations in a post-collisional geodynamic setting. Lithos, 107: 68-92. CONTICELLI S., LAURENZI M.A., GIORDANO G.,
MATTEI M., AVANZINELLI R., MELLUSO L., TOMMASINIS., BOARI E., CIFELLIF. & PERINI G.
(2010) - Leucite-bearing (kamafugitic/leucititic) and-free
(lamproitic) ultrapotassic rocks and associated shoshonites from Italy: constraints on petrogenesis and geodynamics. Journal of the Virtual Explorer, 36(20).
CONTICELLI S., MARCHIONNI S., ROSA D., GIORDANO G., BOARI E. & AVANZINELLI R. (2009b) - Shoshonite and sub-alkaline magmas from an
Ultrapotassic Volcano: Sr-Nd-Pb isotope data on the Roc-camonfina volcanic rocks, Roman Magmatic Province, Southern Italy. Contrib. Mineral. Petrol., 157: 41-63.
CONTICELLI S., MELLUSO L., PERINI G., AVANZINELLIR. & BOARIE. (2004) - Petrologic,
Geo-chemical and Isotopic characteristics of potassic and ultra-potassic magmatism in Central-Southern Italy: inferences on its genesis and on the nature of mantle sources. Perio-dico Mineralogia, 73: 135-164.
CONTICELLIS. & PECCERILLO A. (1992) - Petrology
and geochemistry of potassic and ultrapotassic volcanism in central Italy: petrogenesis and inferences on the evolution of the mantle sources. Lithos, 28(3-6): 221-240.
CORNETTEY., CRISCIG.M., GILLOTP.Y. & ORSIG. (1983) - Recent volcanic history of Pantelleria: a new
in-terpretation. Journal of Volcanology and Geother-mal Research, 17(1-4): 361-373.
COX K., HAWKESWORTH C.J., O’NIONS R.K. & APPLETON J.D. (1976) - Isotopic evidence for the
deriva-tion of some Roman region volcanics from anomalously en-riched mantle. Contrib. Mineral. Petrol., 56: 173-180.
CRAVATTE J., DUFAURE P., PRIM M., & ROUAIX S. (1974) - Les forages du Golfe du Lion: stratigraphie,
sé-dimentologie. Compagnie française des pétroles. CRISCI G.M., DE FRANCESCOA.M., MAZZUOLI R.,
POLIG. & STANZIONE D. (1989) - Geochemistry of
recent volcanics of Ischia Island, Italy: Evidences for frac-tional crystallization and magma mixing. Chemical Geology, 78(1): 15-33.
D’ANTONIO M., CIVETTA L. & DI GIROLAMO P. (1999) - Mantle source heterogeneity in the Campanian
Region (South Italy) as inferred from geochemical and iso-topic features of mafic volcanic rocks with shoshonitic affi -nity. Mineralogy and Petrology, 67(3-4): 163-192. D’ANTONIOM. & DIGIROLAMOP. (1994) -
Petrolog-ical and geochemPetrolog-ical study of mafic shoshonitic volcanics from Procida-Vivara and Ventotene Islands (Campanian Region, South Italy). Acta Vulcanol., 5: 69-80.
D’ANTONIOM., TONARINIS., ARIENZOI., CIVETTA L., DALLAIL., MORETTIR., ORSIG., ANDRIAM. & TRECALLIA. (2013) - Mantle and crustal processes in the
magmatism of the Campania region: inferences from min-eralogy, geochemistry, and Sr-Nd-O isotopes of young hy-brid volcanics of the Ischia island (South Italy).
